Contour lines are one of the most important tools for reading land shape on a flat map. They show elevation, which means height above sea level, and help you picture hills, valleys, ridges, and steep slopes. Learning to read contour lines matters for hiking, planning roads, studying watersheds, and understanding how Earth’s surface changes.
A topographic map turns a three-dimensional landscape into a two-dimensional pattern that can be measured and interpreted.
Key Facts
- A contour line connects points that have the same elevation.
- Contour interval = elevation difference between neighboring contour lines.
- Close contour lines mean a steep slope, while wide spacing means a gentle slope.
- Contour lines never cross on a normal topographic map because one point cannot have two elevations.
- Index contours are darker or thicker lines, often labeled with elevation values.
- Slope = vertical change / horizontal distance, often written as slope = rise / run.
Vocabulary
- Contour line
- A line on a map that connects all locations with the same elevation.
- Contour interval
- The constant elevation difference between one contour line and the next.
- Index contour
- A darker or thicker contour line labeled with its elevation to make the map easier to read.
- Topographic map
- A map that shows the shape and elevation of land using contour lines and symbols.
- Relief
- The difference in elevation between the highest and lowest points in an area.
Common Mistakes to Avoid
- Treating contour lines like roads is wrong because contour lines show equal elevation, not paths for travel.
- Ignoring the contour interval is wrong because the same spacing on two maps can represent very different elevation changes.
- Thinking close lines mean flat land is wrong because close contour lines show rapid elevation change and a steep slope.
- Assuming every closed loop is a hill is wrong because a closed loop with hachure marks shows a depression or basin.
Practice Questions
- 1 A map has a contour interval of 20 m. If one contour line is labeled 300 m, what are the elevations of the next three higher contour lines?
- 2 On a topographic map, a trail rises from 120 m to 300 m over a horizontal distance of 900 m. What is the average slope as rise/run, and what is the slope as a decimal?
- 3 Two routes climb the same hill. Route A crosses contour lines that are very close together, while Route B crosses contour lines that are widely spaced. Which route is likely easier to walk, and why?